The present invention relates to a prosthetic glenoid component for attachment to a glenoid surface of a scapula to replace a natural socket of a shoulder and to provide a bearing surface for a head portion of an arm bone or humerus. More particularly, the present invention relates to a polymeric glenoid component including a body portion having integrally formed attachment legs extending away from the body portion for penetrating the glenoid surface to secure the body portion to the glenoid surface.
The glenoid component of the present invention is designed for use in a total shoulder replacement procedure. In a total shoulder replacement procedure, a humeral component having a head portion is used to replace the natural head portion of the humerus. The humeral component typically has an elongated intramedullary stem to secure the humeral component to the humerus. The glenoid portion of the scapula is resurfaced with a glenoid component which provides a bearing surface for the head portion of the humeral component.
It is known in the prior art to provide glenoid components for replacing a glenoid surface which include plastic inserts coupled to metal trays or backings. The metal backings are used to secure the plastic inserts to the glenoid surface. The backings are typically made from titanium or other suitable metals. The metal backings are typically attached to the glenoid surface using metal fixation screws. An example of a prior art glenoid component using this two-piece glenoid component construction is shown in U.S. Pat. No. 4,865,605.
Several problems arise from the use of two-piece glenoid components. One problem is the possibility of separation of the plastic insert from the metal backing. If such separation occurs, the glenoid component must be replaced. Another problem is that wear of the plastic insert inherently occurs at the interface between the plastic insert and the metal backing. Over time, this wear can cause failure of the glenoid component. Also, the increased thickness required by the metal backing undesirably increases the height of the replacement glenoid surface which can result in stretching and tightening of the soft tissue associated with the shoulder joint.
One object of the present invention is to provide a suitable one-piece glenoid component to eliminate the need for a two-piece glenoid component.
Another object of the present invention is to stabilize the glenoid component to prevent movement of the glenoid component after the glenoid component is attached to the glenoid surface.
Yet another object of the present invention is to provide a glenoid component having integrally formed attachment pegs to facilitate attachment of the component to the glenoid surface.
Still another object of the present invention is to strengthen the bond between the glenoid component and the bone to reduce the likelihood that the glenoid component will become loose after attachment to the glenoid surface.
A further object of the present invention is to provide a thin replacement glenoid surface which does not significantly alter the height of the natural glenoid surface.
According to the present invention, a glenoid component is provided for attachment to a glenoid surface of a scapula to provide a bearing surface for a head portion of a humerus. The glenoid component includes a body portion having a first surface for abutting the glenoid surface and a second surface for providing the bearing surface for the head portion. The glenoid component includes a plurality of attachment legs extending away from the first surface of the body portion for penetrating the glenoid surface to secure the body portion to the glenoid surface. The plurality of attachment pegs are aligned with respect to each other to lie in a single plane The glenoid component includes stabilizing means located on the body portion to engage the glenoid surface to prevent movement of the body portion for stabilizing the body portion when the body portion is attached to the glenoid surface.
In a preferred embodiment of the present invention, the stabilizing means includes first and second stabilizing pegs extending away from the first surface of the body portion for penetrating the glenoid surface to prevent movement of the body portion when the body portion is attached to the glenoid surface. The first and second stabilizing pegs are spaced apart in opposite directions from the attachment peg plane and are aligned with respect to each other to lie in a plane normal to the attachment peg plane.
The attachment pegs and stabilizing pegs are designed to be inserted into a plurality of holes formed in the glenoid surface by a suitable drilling tool. A drill guide may be used to properly align the holes in the glenoid surface. The attachment pegs and stabilizing pegs are secured within the holes drilled into the glenoid surface with bone cement.
Selected ones of the plurality of attachment pegs are formed to include a plurality of serrations for receiving a portion of the bone cement to secure the selected attachment pegs within the holes drilled into the glenoid surface. The stabilizing pegs are also formed to include a plurality of serrations for receiving a portion of the bone cement to secure the stabilizing pegs within the holes drilled into the glenoid surface. The serrations cooperate with the bone cement to increase the strength of the bond between the attachment pegs and the bone.
One feature of the present invention is the provision of a one-piece glenoid component having a body portion including a convex surface which matches the shape of and abuts the glenoid surface and a generally concave surface for providing a bearing surface for a head portion of the humerus. The body portion is integrally formed with a plurality of attachment pegs extending away from the convex surface for securing the body portion to the glenoid surface. The integral configuration of the glenoid component of the present invention eliminates the problem of wear between the plastic insert and the metal backing found in prior art glenoid components. This configuration also eliminates the risk of separation of the plastic insert from the metal backing after installation which is also present in prior art glenoid components. Therefore, the present invention advantageously eliminates the need for a two-piece glenoid component. Because only a single integral component is provided, the glenoid component of the present invention is easier to install than conventional glenoid components and provides a thinner replacement surface which does not significantly alter the natural height of the glenoid surface to prevent undesired soft tissue stretching and tightening.
Another feature of the present invention is the provision of stabilizing pegs extending away from the first surface of the glenoid component. The stabilizing pegs penetrate the glenoid surface to prevent movement of the body portion of the glenoid component when the body portion is attached to the glenoid surface. By positioning the stabilizing pegs in a spaced apart relation from the attachment pegs, the stabilizing pegs advantageously prevent movement of the glenoid component and provide stability to the glenoid component when the component is attached to the glenoid surface. The stabilizing pegs prevent rocking movement of the glenoid component when the humeral head engages the bearing surface of the glenoid component. Additionally, matching the shape of the convex surface with the shape of the natural glenoid surface also acts to increase the stability of the implanted component.
Yet another feature of the present invention is the provision of integrally formed attachment pegs extending away from the body portion of the glenoid component which are formed to include a plurality of notches or serrations for receiving a portion of the bone cement to secure the attachment pegs within the holes drilled into the glenoid surface. Bone cement enters the serrations to increase the contact area between the bone cement and the attachment pegs. This feature advantageously strengthens the bond between the attachment pegs and the bone.
Additional objects, features, and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of a preferred embodiment exemplifying the best mode of carrying out the invention as presently perceived.